Flon R-134a (1,1,1,2-tetrafluoroethane) called new refrigerant is now mainly used as refrigerant for refrigerators, etc., but the future use of the refrigerant is, however, not so promising and will be banned due to a more strict environmental control problem, etc. As a substitute for the refrigerant, hydrocarbon-based gases and a carbon dioxide gas have now been in the spotlight, among which the hydrocarbon gases have a considerably high risk of explosion and combustion, whereas the carbon dioxide gas would be a next-generation refrigerant even according to the world outlook.
However, the carbon dioxide gas is used under higher gas pressure than flon gases and has a higher permeability or solubility through or in the ordinary polymer materials, so that blistering (foaming) will easily occur. Even in a case where no blistering occurs, pressure holding and tight sealing will be hard to maintain, because polymer materials themselves have a high carbon dioxide gas permeability.
Rubber materials usually have likewise a high carbon dioxide gas permeability, which is particularly remarkable under gas pressure of 1 MPa or more, so that the carbon dioxide gas cannot be fully sealed. Furthermore, carbon dioxide dissolves easily into polymers, causing considerable swelling. Accordingly, no rubber material parts have been actually used so far in apparatuses using the carbon dioxide gas.
To solve these problems, a butyl rubber composition comprising butyl rubber and carbon black having a CTAB specific surface area of about 30 -about 100 m2/g has been proposed as a carbon dioxide gas sealing material (JP-A-2002-053718), or a molding material for carbon dioxide use, which comprises chlorinated polyethylene having a chlorine content of 25–47 wt. % or a blend thereof with vinyl chloride-based resin has been proposed as a carbon dioxide sealing material (WO 01/09237) for O-rings, lip seals, etc. These materials have a good carbon dioxide shieldability, but are not satisfactory for heat resistance and wear resistance.
To improve the heat resistance and wear resistance, hydrogenated NBR highly filled with a filler has been proposed (JP-A-2002-080639, JP-A-2002-146342), but its carbon dioxide shieldability is not so high as those of butyl rubber or chlorinated polyethylene.